The averaging of periodic or quasiperiodic signals is nowadays a feature often implemented in various kinds of circuits. For example, an average value of a current multiplied with a supply voltage of a half-bridge circuit can be taken as a measure of an effective power that is output by the half-bridge circuit. The averaging is mostly conducted by means of an RC-filter. The averaging may be also performed by the means of an ADC (analog-to-digital-converter) and a digital filter.
A major disadvantage of the averaging by the means of an RC-filter is that a compromise has to be found between the ripple of the obtained average value and the settling time of the filter. In particular, when closed loop control circuits are considered, the signal delay time has to be short and thus the delay introduced by an RC-filter would significantly affect the achievable control dynamics.
Averaging performed by digital processing would require a very fast ADC due to the high spectral components within the current of the half-bridge circuit. This, however, might lead to a very high current consumption in many applications.
In the light of the problems just described, a circuit for determining an average value is to be provided which, in case it is used in combination with a ADC connected downstream to it, may require only one transformation by the ADC during a half-bridge cycle and further may be able to adjust its output in accordance with changes in the half-bridge current with only a short signal delay.